1. Purpose of the Invention
This invention relates in general to certain new and useful improvements in filtering devices for filtering temperature regulated liquids, and, more particularly, to unique filtering devices and methods of use which permit filtering of high viscosity temperature regulated liquids and which permits close temperature regulation and which is also easily assembled and disassembled.
2. Brief Description of the Prior Art
In the processing of high viscosity, high temperature liquids, and especially thermoplastic and thermosetting polymer melts, it is necessary to pass the liquid plastic melt or other liquid material through filters. These plastic polymers contain many impurities which result in periodic clogging of the filters and therefore the necessary attendant cleaning of the filters. Accordingly, in the processing of these plastic liquid melts, whether monomeric or polymeric, two or more filters in parallel streams are often employed in a process such that one of the filters in one stream may be shut down for temporary cleaning with the other filter being operative in the other process stream. These filters must be effective for purposes of controlling hot thermoplastic or thermosetting liquid melts, particularly of high viscosity, as for example, 1000 poise, and greater.
The filters, as well as the valves and the fluid lines which carry the hot liquid plastic, must be heat sealed. Moreover, the valves and fluid lines must be provided with a means for regulating the temperature of the hot plastic melt during processing. Thus, for example, the various lines which carry the plastic melt may be jacketed for receiving a suitable temperature maintaing or so-called "heat regulating" fluid. In addition, it is necessary to provide filters which contain jackets for receiving a heat regulating liquid to thereby maintain the liquid hot melt at a desired temperature during the processing.
Many of the conventional filters typically employ a jacket disposed over only certain portions of a filter body and which jacket receives a heat regulating fluid typically designed to apply heat to the filter body and hence the plastic liquid melt passing through the filter. This arrangement has not proved to be too effective inasmuch as only certain of the outer portions of the filter body are heated.
U.S. Pat. No. 3,727,767 to Itter et al. proposes a combination filter and valve arrangement in which two parallel filter-valve arrangements are employed. However, one of the major problems with this form of arrangement is that it is quite difficult to shut off the flow to one of the filters while maintaining the flow to the other of the filters. In addition, each filter-valve arrangement is quite complex in its construction, thereby necessitating almost complete disassembly of the valve-filter arrangement in order to clean the filter portion thereof. Notwithstanding the above, it has been found that this form of valve-filter arrangement has not been very effective in maintaining the liquid plastic melt at a desired temperature during the filtering thereof.
In addition to the above, the devices of the type taught in the Itter et al. Patent do not disclose an effective means for providing a temperature controlling fluid to surround the filter while the filtering device is used to process the liquid melt. One of the primary problems in this regard is that most conventional filtering devices do not provide an adequate arrangement for introducing a temperature controlling fluid in order to maintain the liquid melt at a desired temperature during the processing thereof. The Itter et al. Patent is representative of the prior art in that it does not disclose any effective means for maintaining a temperature control fluid surrounding the entire filter valve assembly or at least a substantial portion thereof.
Another one of the primary disadvantages of the filter assemblies of the prior art is that these assemblies are rather complex in their construction and do not provide for easy removal of the filter casing from the filter pot, namely, that is, the housing surrounding the filter. In most of these devices, the filter is actually an integral part of, or otherwise rigidly secured into, a surrounding casing. Thus, the removal of the filter for purposes of cleaning constitutes a rather complex task, and almost always necessitates a complete disassembly of the filter, thereby requiring the complete cessation of processing the hot liquid melt in one side of the processing system.
There have been many proposed dual filter arrangements in addition to that described in the above-cited Itter et al. Patent. For example, in British Patent No. 1,168,063, removable filter pots are employed in the valve with stop cock or rotary slide valve arrangements. One of the principal problems in the aforesaid British Patent, as well as the other prior art valve arrangements, is that after fluid flow is stopped, there is a standing amount of liquid polymer melt contained within the system. This is highly undesirable inasmuch as the standing liquid melt tends to harden and thereby requires almost complete disassembly of the filter system in order to clean the same. Most of the prior art systems do not afford any effective means for removing the remaining liquid melt in the filtering system after it has been turned to the "off" position, thereby stopping the flow of liquid melt therethrough.
In the commercially available filtering devices used with hot liquid melts, the filter casing is designed so that it is capable of being disposed within and rigidly secured to the outer housing. The filter casing is usually either integral with the surrounding outer housing or otherwise rigidly secured thereto in a way that it is not easily or quickly removable therefrom. This construction not only prevents easy removal of the filter casing for purposes of cleaning and replacement of the filter elements, but also interferes with the processing of the hot liquid melt.
Another one of the problems of the prior art devices for use in filtering the hot liquid melts is that it is quite difficult to clean or replace the filter element in the casing after a period of use. Due to the nature of the material being filtered, it is necessary to frequently and periodically replace or clean the filter element. The filter element is usually rigidly affixed to either the filter casing if used or otherwise to the housing, and it is, therefore, difficult to remove the filter element without shutting off the entire system or stream at least for a substantial time period.
Another specific problem in the processing of hot liquid melts resides in the preheating of a filter or filter system used in conjunction with a process for filtering a hot liquid melt. It is generally desirable to preheat the vessel or casing containing the filter element so that is at the ambient temperature of the melt before the filter is introduced into the process stream. In conventional practice, the filter must be introduced in a standard preheating system, that is a system which is provided with a vessel surrounded by a heat regulating fluid in order to heat the filter element to a desired temperature. After the filter has been preheated to the desired temperature, the system in which the hot liquid melt flows is shut down for a short interval while the new filter is installed. This not only interrupts processing of the hot liquid melt, but oftentimes results in other undesirable process discontinuities and process interruptions.